水稻根际芽孢杆菌抗砷胁迫作用及其微生物机制

Microbial Mechanisms of Bacillus Resistance to Arsenite in Rice Rhizosphere

砷甲基化过程作为微生物的砷抗性机制改变砷的毒性和移动性,对土壤砷污染控制有重要意义。砷抗性根际促生菌对砷胁迫下水稻生长产生积极影响,然而水稻根际菌的砷甲基化效率及其影响水稻砷胁迫的机制研究还较为缺乏。从砷污染稻田根际土中筛选出一株砷甲基化功能芽孢杆菌Bacillus sp.LH14,探究该菌株的砷甲基化效率、砷抗性和促生相关特性,以及菌株接种对土壤砷形态、水稻生长和根际微生物相互作用的影响。结果表明,菌株LH14具有砷甲基化和挥发能力,34 h内将三价无机砷转化为甲基砷的效率为54.9%,主要形态为二甲基砷和三甲基砷。LH14接种显著提高了土壤中砷甲基转移酶基因(arsM)丰度,增加土壤溶液甲基砷浓度,表明LH14参与了土壤砷形态转化。LH14能在砷胁迫下产生吲哚-3-乙酸(IAA),菌株浸染显著增加高砷条件下种子萌发率、根和芽长及生物量。接种LH14对砷污染土壤中水稻植株生长有促进作用,可能与根际有益菌(例如Burkholderiaceae和Gemmatimonadaceae)相对丰度增加有关。所以,水稻根际存在砷甲基化功能植物促生菌,接种该菌改变水稻根际砷形态,并能产生植物激素和富集根际有益菌从而直接和间接地促进水稻生长,有利于缓解水稻砷胁迫,为砷甲基化功能菌应用于砷污染土壤修复和缓解植物砷胁迫提供理论支撑。

【Objective】Microbial arsenic(As)methylation is a vital As resistance mechanism that alters the toxicity and mobility of As,and can be used for the control of As contamination in soils.As-resistant plant growth-promoting bacteria use this mechanism to positively affect the growth of rice in As-contaminated soil.However,the arsenic methylation efficiency of rice rhizosphere bacteria and its effect on rice growth under arsenic stress remain unclear.【Method】In this study,an As-methylating functional Bacillus sp.LH14 was isolated from rice rhizosphere soil contaminated with As.The As methylation efficiency,As resistance and plant growth-promoting traits of the strain were analyzed.Additionally,the effect of strain inoculation on rice growth,rhizosphere As species and microbial interactions in As-contaminated soil were explored.【Result】The results show that strain LH14 promoted As methylation and volatilization and produced dimethylarsenate and trimethylarsenic oxide,which accounted for 54.9%of the initial As(Ⅲ)in the medium.LH14 inoculation significantly increased the copy numbers of arsenic methyltransferase gene(arsM)and methylated As in rhizosphere soil,indicating that LH14 was involved in soil As transformation.LH14 produced IAA under As stress and significantly increased seed germination rate,root and shoot length and biomass in the presence of high As concentration.Also rice growth in the soil was significantly promoted by LH14 inoculation,and this was associated with the enrichment of beneficial microorganisms(e.g.,Burkholderiaceae and Gemmatimonadaceae)in the rhizosphere.【Conclusion】Inoculation with As-methylating plant growth-promoting bacteria altered As speciation in rice rhizosphere and directly or indirectly promoted rice growth by producing plant hormones,enriching beneficial bacteria,and alleviating As stress.These findings provide theoretical support for the application of As-methylating bacteria in the remediation of As-contaminated soil and alleviation of As stress in plants.